1. Field of the Invention
The present invention relates to a plasma processing apparatus which is suitably usable when an object to be processed is subjected to various plasma treatments for the purpose of manufacturing an electronic device, etc.
2. Background Art
In general, a plasma processing apparatus according to the present invention is widely applicable to various kinds of plasma processing procedures, which include the production of materials for electronic device such as semiconductors or semiconductor devices, and liquid crystal devices. For the convenience of explanation, however, the background art relating to semiconductor devices will be described below.
In general, in the processes for manufacturing semiconductor devices, a base material or substrate (such as wafer) for semiconductor devices as an object to be processed is subjected to various kinds of treatments such as CVD (chemical vapor deposition), etching, and sputtering.
Hitherto, there have been many cases wherein plasma processing apparatuses are used for conducting such various kinds of treatments. This is because, when the plasma processing apparatus is used, the base material can be processed while maintaining the base material at a relatively low temperature.
For example, when microwaves are used for conducting plasma treatments, it is a common procedure that a dielectric material is disposed between an antenna for emitting microwave, and a plasma processing chamber wherein the object to be processed is to be plasma-treated, for the purpose of maintaining the sealing condition in the inside of the plasma processing chamber.
In a case where such plasma processing is conducted under a certain condition, there can be generated an electromagnetic field (or surface wave) which propagates along the interface (i.e., plasma boundary region) between the above-mentioned dielectric material and the plasma which has been generated on the basis of the microwave irradiation. According to the investigations and knowledge of the present inventors, for example, it has been found that, when the plasma density is increased to an extent that the sheath region becomes negligible, the surface wave is generated depending on the microwave frequency, the dielectric constant of the dielectric material, and the electron density of the plasma.
When such surface wave is generated, surface wave plasma (SWP) is also generated in the inside of the plasma processing chamber, and there occurs a problem that a mode peculiar to the wave motion is provided.
Therefore, in view of the uniformity in the plasma and in the process utilizing the plasma, it has been demanded to suppress the generation of such surface waves.
Hitherto, in order to suppress the generation of the surface wave plasma, there have been taken roughly two kinds of measures: (1) a measure wherein the propagation of surface wave is obstructed; and (2) the generation of the surface wave per se is inhibited.
For example, a plasma processing apparatus wherein a metal member is disposed in the plasma boundary region is known, as one of the measures for obstructing the propagation of the surface wave according to the above method (1).
However, when a metal member is disposed in the plasma boundary region, unnecessary dust, particles, etc., are produced in the plasma processing chamber due to the sputtering phenomenon in the site where the plasma comes into contact with the metal member, whereby the process performance of the plasma processing can be greatly deteriorated.